Self-healing technology has taken another step forward with the announcement that a research team has developed a self-healing battery. The breakthrough could mean significantly longer lifespans for batteries in devices or electric cars.

The research team, from University and the Department of Energy's SLAC National Accelerator Lab, described in a paper published this week in Nature Chemistry magazine that they used a silicon electrode in a lithium ion battery, instead of the normal carbon electrode in that role. Silicon can store 10 times more lithium than carbon, and thus create a longer battery life, but silicon usually swells up and shrinks during every charge cycle. This expansion and contraction causes the silicon electrode to crack and disintegrate.

The team used a synthetic polymer whose hydrogen-bond formation can heal the cracks in the silicon, allowing the silicon to last 10 times longer than without the polymer. Carbon nanoparticles were also added so the polymer would be able to conduct electricity.

Weakened Chemical Bonds

The scientists weakened some chemical bonds in the polymer so that it could be used to heal the silicon. The weakened polymer breaks more easily than before, but the chemical bonds can also link up again more easily, a process that resembles how DNA can rearrange and recombine.

Stanford associate professor Yi Cui told news media that this approach could "make silicon workable for the battery electrode," by repairing any cracks within a few hours.

Cui and his team developed this approach after learning that another Stanford research team was working on the creation of an interactive sensor network, or "skin," of flexible plastic. This led Cui's team to ask: "Why can't we combine a self-healing polymer together with a battery?" In fact, the self-healing battery was developed in the same lab as the flexible, sensor-laden "skin," which could eventually be used for robots or prosthetic limbs.

The polymer-covered battery electrodes can currently work for about 100 charge/discharge cycles, but the goal is 500 cycles for cell phones and 3,000 for electric vehicles. A cycle is when a battery delivers 100 percent of its charge and then recharges fully.

Other Self-Healers

The self-repairing battery is the latest of several announced breakthroughs in self-healing electronic technology. In March, for instance, researchers from the California Institute of Technology developed, for the first time, a method for chips to route circuits around damaged components in order to "heal" themselves.

These healing chips contained a number of on-chip sensors that monitor temperature, current, voltage and power, feeding updates to a custom-made application-specific integrated circuit (ASIC) on the same chip. When there are changes in the expected measurements that indicate damage, the ASIC finds the best alternative routing through actuators on the chip, out of more than 250,000 possible configurations.

At the end of 2011, a research team at the University of Illinois utilized microcapsules that reside above a gold circuit line. When a crack developed in the circuit, the microcapsules released liquid metal to repair the break -- within a hundred microseconds.